In the related art, a large amount of data is stored in a RAID system having a plurality of disks. The RAID system further includes a cache for storing the data provisionally, and is utilized for various processes.
The RAID system uses the cache, for example, in the case where the copy process is executed to protect the data written in a disk. The RAID system uses the cache also to accept a data write request from a host computer. Referenced documents are Japanese Laid-Open Patent Publication No. 2004-102815 and 2003-345524.
The conventional RAID system poses the problem that the copying speed is reduced.